Crosstalk between the immune and reproductive systems dramatically impacts fertility. In particular, studies have shown that a tight spatiotemporal control of leukocyte infiltration into the ovary is pivotal for successful ovulation. Once infiltrated, the leukocytes differentiate into a cohort of pro- or anti-infiammatory cells in the preovulatory ovary and play critical roles in ovulation and luteal formation. In this study, we will test the hypothesis that progesterone (P4) and prostaglandins (PG) play pivotal roles in recruiting leukocytes into the preovulatory ovary. Aim 1. To determine the mechanism(s) by which P4 and PG regulate WBC infiltration. We will first determine the roles of P4 and PG on WBC infiltration by treating cycling adult rats with RU486, indomethacin and vehicle, and measuring the effect on the numbers, populations and localization of infiltrating WBC by flow cytometry and immunohistochemistry together with a functional analysis of the expression of chemokines, cytokines, their receptors and cell adhesion molecules (CAMs) in serum, on ovarian cells and WBC by ELISA and qPCR. Aim 2. To determine whether P4 and PG regulate WBC infiltration in primate ovary. In this Aim, we will investigate P4 and PG regulated WBC infiltration in primates. Similar to rodents, primates, including humans also require P4 and PG for normal ovulation. Therefore, we hypothesize that P4 and PG will regulate WBC infiltration in the primate ovary. The actions of P4 and PG will be inhibited by treating primates (Cynomolgous monkeys) with trilostane (3|3HSD inhibitor; inhibits progesterone synthesis), celecoxib (selective COX-2 inhibitor) or vehicle under ovarian stimulation. The effects on the numbers, populations and localization of WBC together with the expression of infiammatory mediators will be determined. Upon the identification of the P4- and PG-regulated WBC subtypes and infiammatory mediators in the monkey, the localization and expression patterns of their homologs will be determined in the human ovary. Aim 3. To determine the regulatory mechanism of preovulatory splenic WBC release. We will identify the trigger(s) and the mechanism of action of splenic WBC release from spleen. We hypothesize that either LH, decreased concentration of circulating WBC or angiotensin-ll (the only known trigger of splenic leukocyte release) act as the trigger. To identify the trigger(s), ovariectomized rats will be treated with candidate triggers (LH and angiotensin-ll) or artificially reduce the concentration of circulating WBC by perfusing rats with plasma. The effects on splenic WBC release will be measured by counting WBC numbers in spleen and peripheral blood.